LINQ is just an "express your query as an AST" approach. Sure LINQ presents its self as a DSL on top of that AST ( which is exactly what SQL is at the end of the day ), but there are libraries for MongoDB that allow you to do the same thing. There is even a LINQ driver for MongoDB[1]. What you are missing is that by having the lowest common denominator be the AST instead of a DSL you have removed a huge burden from both the server and client side of the operation. From that AST you can build any kind of client side interface without worry about how to parse or compile the result into a specific textual language, even plain old SQL[2] can be used if you like your sever spending its clock cycles parsing text.

1. http://mongodb.github.io/mongo-csharp-driver/2.1/reference/d... 2. https://www.progress.com/connectors/mongodb

I like mongo's interface (most of the time)... but when you get to more interesting queries, it gets far more weird than even SQL... I wrote an early node API almost mirroring the JSON query interface (was easy enough to do filtering on sensitive fields), and it worked really well.

That said, it was really clunky dealing with ordering as JSON doesn't guarantee serialization order (sort fields), and that was cumbersome to work around iirc...

Today RethinkDB would be my first choice for a similar solution... better ops interfaces with replication + failover. Instead of having to do a replica of a sharded system in mongo for distribution with redundancy. Also, while the query interface is a little more complicated to get started with, when your queries get more interesting, it's not nearly as messy as mongo gets.

> or any other "express-your-query-as-an-AST" approach

Well SQL is just an AST abstraction, which was made to be human readable. And that's exactly the issue, SQL is excellent for humans to express querys but really inconvenient to interface with other programs unless you express every single query ad-hoc (which seems the way most people choose since ORM tend to perform poorly)